There is a growing demand for antimicrobial cleansing compositions. Antimicrobial soap bars and cleansers for hand and body are increasingly being preferred by consumers.
Antimicrobial cleansing compositions containing oligodynamic metal like silver, copper or zinc are very effective against a variety of bacteria. Silver is used most widely. However some metals, especially silver, are particularly prone to destabilisation upon exposure to high pH, heat and strong sunlight discolouration, agglomeration or even phase separation under extreme conditions.
Usually such metals are included at ppm or even ppb (parts per million/parts per billion) levels which make it imperative to ensure that the least amount is rendered inactive.
It generally is also difficult to ensure uniform distribution of silver within the matrix of the composition.
This led to the development of aqueous premix compositions which are used as delivery vehicles.
The liquidy base of such compositions makes it easy to dose and distribute the oligodynamic metal with greater precision.
However discoloration, especially of Silver is still a problem, as some of the known methods do not provide a robust, effective and long-lasting solution.
US2006240122 A1 (Miner Edwin) discloses that polypectate and EDTA (a chelator) can be used to stabilise silver ions and prolong the antimicrobial effect. It is also disclosed that chelated silver disperses better than non-chelated silver. The polypectate chelates with free calcium and magnesium ions. The complex is prepared by first preparing an ammoniacal silver nitrate mixture. The application also discloses a liquid antiseptic composition containing water, silver ions, polypectate and EDTA.
US2012034314 A1 (Levison Lisa Turner) discloses that a fixative polymer Polyquaternium-69 can bind the chelated metal ions to the skin for an extended period. The chelated silver compound (e.g. silver acrylate) is suspended in the polymer to form a tacky liquid.
US2011224120 AA (Henkel) discloses that silver ions can be stabilised by using non-neutralized fatty acids.
US 2010/0143494 (Clorox) discloses an antimicrobial composition containing a soluble silver salt and an alkanolamine or aminoalcohol. The composition may additionally contain an amino acid or amino acid salt and surfactant. The composition has additional stability and activity compared to prior art silver complexes.
There is an unmet need for a robust solution for the technical problem of discolouration. There is also a need for a solution for the problem of instability.